When do women typically start to show?

Depends. It depends on your body type, weight, gestational age and number of previous babies. Some women may show as early as 12-14 weeks while other will be later around 16-18. By 20 weeks it is usually very obvious to everyone:).
20 weeks. Although this may differ depending on the body types of people, pregnant women will typically start to show around 16-22 weeks of pregnancy.